Method and apparatus for controlling data read/write between a hard disk and a hard disk controller

ABSTRACT

A position error signal amplitude indicative of the distance between an expected position of a magnetic head relative to the track centerline of a magnetic data storage and retrieval system and an actual position of the magnetic head relative to the track centerline is detected and filtered. The signal is filtered to generate a sway mode signal amplitude indicative of an oscillation of the actual position of the magnetic head relative to the track centerline in the frequency range of the filter. The absolute value of the sway mode signal amplitude is then determined. If the absolute value of the sway mode signal exceeds a predetermined threshold value that correlates to a high probability of impending a head-disk crash, a warning signal is propagated. Alternative embodiments similarly predict the possibility of head-disk crash on the basis of the maximum value of several samples of the position error signal and on the basis of the maximum value of several samples of the square of the position error signal amplitude

RELATED PATENT APPLICATION

This Divisional Application claims the priority of parent applicationSer. No. 09/909,294, filed on Jul. 19, 2001, now U.S. Pat. No.6,683,737, and entitled “Method and Apparatus for Predictive FailureAnalysis Technique for Head Crashes in Hard Drives Using Mechanical SwayMode Detection.”

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates in general to magnetic data storage andretrieval systems and in particular to methods and apparatus forpredicting head-disk interactions in magnetic disk storage and retrievalsystems. Still more particularly, the present invention relates to animproved method and apparatus for predicting head-disk interactions(e.g. head crashes) in magnetic disk storage and retrieval systems onthe basis of sway mode frequency presence in a position error signal.

2. Description of the Related Art

Generally, a data access and storage system consists of one or morestorage devices that store data on magnetic or optical storage media.For example, a magnetic data storage and retrieval system is known as adirect access storage device (DASD) or a hard disk drive (HDD) andincludes one or more disks and a disk controller to manage localoperations concerning the disks. The disks themselves in a hard diskdrive (HDD) are usually made of aluminum alloy or a mixture of glass andceramic, and are covered with a magnetic coating. Typically, two or moredisks are stacked vertically on a common spindle that is turned by adisk drive motor at several thousand revolutions per minute (rpm).

The only other moving part within a typical magnetic data storage andretrieval system is the actuator assembly. Within most magnetic datastorage and retrieval systems, the magnetic read/write head is mountedon a slider. A slider generally serves to mechanically support the headand any electrical connections between the head and the rest of the diskdrive system. The slider is aerodynamically shaped to glide over movingair in order to maintain a uniform distance from the surface of therotating disk, thereby preventing the head from undesirably contactingthe disk.

Typically, a slider is formed with an aerodynamic pattern of protrusions(air bearing design) on its air bearing surface (ABS) that enables theslider to fly at a constant height close to the disk during operation ofthe disk drive. A slider is associated with each side of each diskplatter and flies just over the platter's surface. Each slider ismounted on a suspension to form a head gimbal assembly (HGA). The HGA isthen attached to a flexible suspension, which is attached to a rigidarm. Several arms are ganged together to form a head/suspension/armassembly.

Each read/write head scans the surface of a disk during a “read” or“write” operation. The head/suspension/arm assembly is moved utilizingan actuator that is often a voice coil motor (VCM). The stator of a VCMis mounted to a base plate or casting on which the spindle is alsomounted. The base casting is in turn mounted to a frame via a compliantsuspension. When current is fed to the motor, the VCM develops force ortorque that is substantially proportional to the applied current. Thearm acceleration is therefore substantially proportional to themagnitude of the current. As the read/write head approaches a desiredtrack, a reverse polarity signal is applied to the actuator, causing thesignal to act as a brake, and ideally causing the read/write head tostop directly over the desired track.

In normal operation, the slider and head fly over the surface of thedisk at a vertical height on the order of 2 millionths of an inch. Themicroscopic distance between the recording surface and the read/writehead leaves little tolerance for vertical misalignment. Even very smallangular misalignments of components resulting from wear, mismanufacture,or foreign objects on the surface of the disk can cause the head to comein contact with the recording surface. Such physical contact may causethe slider to “fishtail” temporarily in the plane of the disk surface.Repeated physical contacts in the same location on the disk surface maylead to a head-disk crash. This renders the disk inoperable and destroysany data stored on the recording surface.

Computer users have traditionally, if bitterly, accepted as inevitablethe random loss of data due to a head-disk crash. Frequent backups limitthe magnitude of data loss, but no convenient and cost-effectivesolution exists for entirely preventing the loss of data. Greater backupfrequency reduces the magnitude of the loss but increases the magnitudeof the inconvenience to the user. Redundant storage solutions reducedata loss but degrade system performance and increase system cost. Usershave long desired, and industry has unsuccessfully attempted to produce,a warning that would inform users of an impending head-disk crash. Witha proper warning of an impending head-disk crash, users could perform animmediate backup of desired data and thereby completely eliminate dataloss from head-disk crash events.

SUMMARY OF THE INVENTION

It is therefore one object of the present invention to provide a methodand apparatus for improved warning of head-disk crash in magnetic datastorage and retrieval systems.

It is another object of the present invention to provide a method andapparatus for predicting head-disk crash events in magnetic data storageand retrieval systems.

It is yet another object of the present invention to provide a methodand apparatus for predicting head-disk crash in magnetic data storageand retrieval systems on the basis of sway mode or fishtailing frequencybehavior in a position error signal.

The foregoing objects are achieved as is now described. A position errorsignal (PES), indicative of the distance between an expected radialposition of a magnetic head relative to a particular track centerline ofa magnetic data storage and retrieval system and an actual position ofthe magnetic head relative to the recording surface, is detected andfiltered. The signal is bandpass filtered to generate a sway mode(fishtailing) signal indicative of an oscillation of the actual positionof the magnetic head relative to the track centerline. The absolutevalue of the sway mode signal is then determined. If the absolute valueof the sway mode signal exceeds a predicted threshold value thatcorrelates to a high probability of an impending head-disk crash, awarning signal is propagated. Alternative embodiments similarly predictthe possibility of head-disk crash on the basis of the maximum value ofseveral samples of the position error signal and on the basis of themaximum value of several samples of the square of the position errorsignal.

The above as well as additional objects, features, and advantages of thepresent invention will become apparent in the following detailed writtendescription.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the invention are setforth in the appended claims. The invention itself, however, as well asa preferred mode of use, further objects and advantages thereof, willbest be understood by reference to the following detailed description ofan illustrative embodiment when read in conjunction with theaccompanying drawings, wherein:

FIG. 1 depicts a schematic drawing of one embodiment of a magnetic datastorage and retrieval system for a data processing system, in which apreferred embodiment of the present invention may be implemented;

FIG. 2A is a simplified top view of an exemplary data storage disk inaccordance with a preferred embodiment of the present invention;

FIG. 2B depicts a simplified view of a small section of an exemplarydata storage disk in accordance with a preferred embodiment of thepresent invention;

FIG. 3 illustrates the fishtailing of a slider caused by a physicalcontact between the slider and the disk surface, while the disk drive isin a track-following mode.

FIG. 4 is a high-level schematic of a control circuit for magnetic datastorage and retrieval system in accordance with a preferred embodimentof the present invention;

FIG. 5 depicts a high-level flowchart for the process of predicting andwarning of an impending head-disk crash in accordance with a preferredembodiment of the present invention;

FIG. 6 is a high-level schematic of a data storage structure inaccordance with an alternative embodiment of the present invention;

FIG.7 depicts a high-level flowchart for a process of predicting andwarning of an impending head-disk crash on the basis of the absolutevalue of the position error signal in accordance with a firstalternative embodiment of the present invention; and

FIG. 8 is a high-level flowchart for a process of predicting and warningof an impending head-disk crash on the basis of the square of theposition error signal in accordance with a second alternative embodimentof the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

With reference now to the figures, and in particular with reference toFIG. 1, a schematic drawing of one embodiment of a magnetic data storageand retrieval system for a data processing system, in which a preferredembodiment of the present invention may be implemented, is illustrated.The magnetic data storage and retrieval system 100 has an outer casting,housing or base 102 containing a plurality of stacked, parallel magneticdisks 104 (one shown), which are closely spaced apart. Disks 104 arerotated by a spindle motor located there below about a central drive hub106. An actuator 108 comprises a plurality of stacked, parallel actuatorarms 110 (one shown) in the form of a comb that is pivotally mounted tothe base 102 about a pivot assembly 112. A controller 114 is alsomounted to the base 102 for selectively moving the comb of arms 110relative to disks 104. The controller 114 monitors and provides commandinputs to the actuator 108.

In the embodiment shown, each arm 110 has extending from it a pair ofparallel, cantilevered load beams or suspensions 116 (one shown), and atleast one magnetic read/write transducer or head 118 mounted on a slidersecured to a flexure that is flexibly mounted to each suspension 116.The read/write heads 118 magnetically read data from and/or magneticallywrite data to the disks 104. The level of integration called a headgimbal assembly comprises a head 118 mounted on a suspension 116.Suspensions 116 have a spring-like quality which biases or maintainsthem in parallel relationship relative to one another. A voice coilmotor 120 housed within a conventional voice coil motor magnet assembly(not shown) is also mounted to the arms 110 opposite head gimbalassemblies 116. Movement of an actuator coil assembly 122 (indicated byarrow 124) moves the head gimbal assemblies 116 substantially radiallyacross tracks on the disks 104 until the heads on assemblies 118 settleon the target tracks. The head gimbal assemblies 116 operate in aconventional manner and always move in unison with one another, unlessthe hard drive 100 uses a split actuator (not shown) wherein the armsmove independently of one another.

The controller 114 will typically include a closed-loop actuator servocontrol system for positioning the actuator and the read/writetransducers to specified storage track locations on the data storagedisk. During normal data storage system operation, a servo transducer,generally mounted proximate to the read/write transducers in the head118, or, alternatively, incorporated as part of the read element of thetransducer in the head, is typically employed to read information forthe purpose of following a specified track (track following) and seekingspecified track and data sector locations on the disk (track seeking).

With reference to FIG. 2A, a simplified top view of an exemplary datastorage disk in accordance with a preferred embodiment of the presentinvention is depicted. Details of an exemplary servo control techniquewill be described with reference to this exemplary data storage disk.The exemplary servo technique and disk are illustrated for purposes ofexample and not of limitation; a number of servo control techniques anddisks used therein are covered by the present invention. As shown inFIG. 2A, the exemplary disk 200 generally includes a number ofconcentric tracks 202 which are generally divided into a plurality ofsectors 204. Each of the sectors 204 generally includes a servoinformation field 206 and a data field 208. Each servo information field206 may consist of a number of subfields including, for example, asynchronization field, a Gray code field and a servo pattern field. Forease of illustration, only a servo pattern field is shown herein. Ingeneral, the servo information fields 206 induce readback signals in aread head. The readback signals are then demodulated to generate aposition error signal (PES signal) which can, for example, be used toposition the read transducer at the centerline of a desired track 202.

A servo track writing procedure will typically be implemented toinitially record servo pattern information 206 on the surface of one ormore of the data storage disks 300. A servo track writer (STW) assembly(not shown) is typically used by manufacturers of data storage systemsto facilitate the transfer of servo pattern data 206 to one or more datastorage disks 200 during the manufacturing process.

In accordance with one known STW technique, embedded servo informationfields 206 are written to the disk along segments extending in adirection generally outward from the center of the disk to embed a servopattern. The embedded servo pattern is thus formed between the datafields 208 of each track. It is noted that a servo information field 206typically contains a pattern of data, often termed a servo burstpattern, used to generate a position error signal (PES) to maintainoptimum alignment of the read/write transducers over the centerline of atrack when reading and writing data to specified sectors 208 on thetrack. The servo information field 206 may also include sector and trackidentification codes which are used to identify the coarse position ofthe transducer.

The servo burst pattern typically induces signals in the read element(readback signals) of the head 118 which are used to develop a positionerror signal (PES). The PES is used to maintain the transducer in thehead 118 over the centerline of the track 202.

With reference to FIG. 2B, a simplified view of a small section of anexemplary data storage disk in accordance with a preferred embodiment ofthe present invention is illustrated. FIG. 2B illustrates a read head200 flying over an enlarged portion 202 of a data storage disk 200. Thedisk portion 202 generally includes a servo information field 204, atleast a portion of which is divided into servo patterns. While theinvention is not so limited, two patterns, an A field pattern 206 and aB field pattern 208, are provided in the illustrated embodiment. The Aand B servo field patterns 206 and 208 are read by the read head 200 andthe induced readback signals are demodulated and used for positioningthe read heads. As each read head passes over the servo informationfield 204, two readback signals e_(a) and e_(b) are induced by servopattern A 206 and servo pattern B 208, respectively. The inducedreadback signals e_(a) and e_(b) are then demodulated to develop aposition error signal (PES), for example, according to the relationship:PES=(e_(b)−e_(a))/(e_(b)+e_(a)). The PES signal is provided to the servocontroller 114, which in conventional systems moves the read head 118 tomaintain the PES signal equal to zero during track following. A moredetailed discussion of servo information patterns and servo controlsystems may be found in Narita et al., U.S. Pat. No. 5,426,544, entitled“Sensitivity Correcting Circuit Of Servo Signal Detection On DataSurface And Offset Measuring Circuit And Magnetic Disk Unit,” andSuzuki, U.S. Pat. No. 5,457,587, entitled “Method And System ForCorrecting Offset Of Head Position Signal,” both of which are hereinincorporated by reference.

FIG. 3 depicts an isolated track 310 on a disk surface 300 of a harddisk drive 100. The disk surface is rotated in the counterclockwisedirection and the head/slider 118 is following the center line of thetrack 310. A physical head-disk contact is made at point 312 causing theslider to move from side to side in a damped fashion in the plane of thedisk surface. This is often referred to as the slider being in afishtail mode or a swaying mode. A footprint 314 of the head centerlinerelative to the centerline of the track 310 is shown as the dashed linein FIG. 3. The fishtail mode event of the head 118 is temporary; itstarts at the point 312 on the track 310 and ends at a point 316 on thetrack 310. The duration of the fishtailing event depends on the severityof the head-disk impact and may last for several revolutions of thedisk. The fact that this fishtailing motion is in the plane of the disksurface allows its detection in the position error signal (PES).

With reference to FIG. 4, a high-level schematic of the control circuitfor magnetic data storage and retrieval system in accordance with apreferred embodiment of the present invention is depicted. The controlcircuit 400 includes an arm-electronics (AE) module 402 receiving areadback signal from the head 118 on a line 401. The output signal ofthe AE module 402 is sampled (sampler not shown) and the sampled signalx(n) is presented to a demodulator 404 on a line 403. The demodulator404 produces a position error signal, PES(k), where k is the servo indexcorresponding to one of the servo fields 206 in FIG. 2A. The PES(k)signal on a line 405 is fed into a servo controller 408 that provides acontrol output U(k) relative to its input PES(k). The servo controller408 contains a servo control algorithm and may also have one or morenotch filters to filter out mechanical resonance frequencies present inthe control output U(k). The digital control output U(k) is converted toan analog signal in a Zero Order Hold (ZOH) 412 whose output isamplified by an amplifier 420. The amplifier 420 provides a signal on aline 422 to an actuator 410, which is typically a voice motor (VCM). Theactuator 410 repositions the head/suspension/arm assembly to moreperfectly align the head 118 to the centerline of the track 310 on thesurface 300 of the disk 200. This description completes the closedactuator servo-loop in FIG. 4.

Also shown in FIG. 4 is the sway mode or fishtail mode detectionapparatus. The position error signal PES(k) on the line 405 is filteredby a programmable bandpass filter 418 tuned to accept the sway-modefrequencies for a given type of slider/suspension assembly. The filteredoutput from the bandpass filter 418 is rectified and smoothed by arectifier 422. The output of the rectifier 422 is called a sway modesignal 424 and indicates an oscillation of the actual position of themagnetic head 118 relative to the centerline of the recorded track 310.The sway mode frequency is an empirically determined frequency at which,if oscillations of the actual position of the magnetic head relative tothe recording surface in the selected frequency range are present, ahead-disk interaction is likely. The sway mode signal 424 thenpropagates to a comparison module 426, which compares the sway modesignal 424 to a reference signal 428 that is stored in a thresholdmodule 430. If the comparison module 426 determines that the strength ofthe sway mode signal exceeds the strength of the reference signal 428,then a failure warning 432 is generated and sent outside the circuit.

With reference to FIG. 5, a high-level flowchart for the process ofpredicting and warning of an impending head-disk crash in accordancewith a preferred embodiment of the present invention is illustrated. Theprocess begins at step 500, which depicts an initiation sequence. Insome embodiments of the invention, the initiation sequence will involvewaiting for the hard drive to enter its idle time function, or theprocess may be triggered by other system events ranging from an internaltiming trigger to manual input from a user of the system. After theprocess has been triggered and the initiation sequence portrayed in step500 has run, the process then passes to step 502, which illustrates thedetection of a position error signal indicative of the distance betweenan expected position of a magnetic head relative to a track centerlineand an actual position of the magnetic head relative to the trackcenterline. The process next passes to step 504, which depicts thebandpass filtering of the position error signal to generate a sway modesignal indicative of an oscillation of the actual position of themagnetic head relative to the track centerline in a selected frequencyrange.

This embodiment of the invention functions on the basis of an observedcorrelation between the presence of oscillations of the position errorsignal in a selected frequency range and the occurrence of disk-headcontact. For magnetic data storage and retrieval systems, there exists aunique selected frequency or discrete range of selected frequencieswherein, if the position error signal oscillates substantially in thatselected frequency range, a high likelihood of head-disk crash exists.The presence of oscillations in the empirically derived selectedfrequency range serves as a precursor to magnetic data storage andretrieval system failure, and the filtering step 504, serves to isolatefor further examination the oscillations of the position error signal inthat selected frequency range.

The process next passes to step 506, which illustrates determining anabsolute value of the sway mode signal, and then passes to step 508,which depicts determining whether the absolute value of the sway modesignal exceeds a threshold value. Though some oscillations in theselected frequency range may exist at all times, the correlation betweenthe oscillations of the position error signal in the selected frequencyrange and the likelihood of a head-disk crash increases with theabsolute value of the position error signal in the selected frequencyrange, and the threshold value to which the determining step comparesthe absolute value of the position error signal in the selectedfrequency range represents a point at which the absolute value of theposition error signal in the selected frequency range correlates to ahigh likelihood of head-disk crash. Once the selected frequency rangefor a particular drive or family of drives has been determined throughtesting, it may be stored in a programable filter. A non-programmablefilter may also be used during production if the selected frequencyrange is already known at the time of manufacture.

If the absolute value of the sway mode signal exceeds the thresholdvalue, the process next passes to step 510, which illustratespropagating a warning signal. This warning signal, a predictive failureanalysis warning, informs the system of the likelihood of a head-diskcrash. Once this signal is activated, the system can then take automaticmeasures to prevent data loss or can prompt the user with a predictivefailure warning and instruct the user to take measures to protect theuser's data. Measures that may be taken manually or automaticallyinclude performing a backup of the magnetic data storage and retrievalsystem in question, discontinuing access to the disk and shutting downthe disk, or shutting down the data processing system in which themagnetic data storage and retrieval system operates. The appropriatedata loss prevention measures will vary on the basis of the operationalrequirements and environment of the data processing system to which themagnetic data storage and retrieval system is attached. If the absolutevalue of the sway mode signal does not exceed the threshold value, theprocess next passes to step 500, which depicts an initiation sequence.In some embodiments of the invention, the initiation sequence willinvolve waiting for the hard drive to enter its idle time function, orthe process may be triggered by other system events ranging from aninternal timing trigger to manual input from a user of the system.

With reference to FIG. 6, a high-level schematic of a data storagestructure in accordance with an alternative embodiment of the presentinvention is depicted. The data storage structure 600 includes severalstorage levels 602-606, each of which contains several data points608-620. The alternative embodiments of the present invention willtypically employ the data storage structure 600 to store samples of theabsolute value or the square of the position error signal as data points608-620. Those samples of the absolute value or the square of theposition error signal (PES) will typically be written to the data points608-620 of one or more storage levels 602-606 for a given length of timeand then read from the data points 608-620 of one or more storage levels602-606. The maximum of the data points 608-620 will then typically bedetermined from the PES values read. Though the data storage structure600 described herein contains only three storage levels 602-606 and eachstorage level 602-606 contains seven data points 608-620, the number ofstorage levels 602-606 and data points 608-620 will vary on the basis ofthe design requirements of a particular embodiment, and the design shownhere is merely illustrative of a typical example.

With reference to FIG. 7, a high-level flowchart for a process ofpredicting and warning of an impending head-disk crash on the basis ofthe absolute value of the position error signal (PES) in accordance witha first alternative embodiment of the present invention is illustrated.The process begins at step 700, which depicts an initiation sequence. Insome embodiments of the invention, the initiation sequence will involvewaiting for the hard drive to enter its idle time function, or theprocess may be triggered by other system events ranging from an internaltiming trigger to manual input from a user of the system. After theprocess has been triggered and the initiation sequence portrayed in step700 has run, the process then passes to step 702, which illustrates thedetection of a position error signal indicative of the distance betweenan expected position of a magnetic head relative to the track centerlineand an actual position of the magnetic head relative to the trackcenterline. The process next passes to step 704, which depictsdetermining an absolute value of the position error signal.

This embodiment of the invention functions on the basis of an observedcorrelation between the absolute value of the position error signal andthe occurrence of disk-head crash. For many magnetic data storage andretrieval systems, if the absolute value of the position error signalexceeds a given value, a high likelihood of head-disk crash exists. Thatthe absolute value of the position error signal exceeds a given valueserves as a precursor to magnetic data storage and retrieval systemfailure.

The process next passes to step 706, which illustrates storing theabsolute value of the position error signal. The position error signalwill typically be stored in a data structure 600 such as that portrayedin FIG. 6. In a typical embodiment, each of several storage levels602-606 will represent one or more testing periods, each of which willcontain several data points 608-620. A typical embodiment will involvethe placement of a series of data points 608-620 in one or more storagelevels. In step 706, the process stores an individual absolute value ofthe position error signal in an individual data point. The process thenpasses to step 708, which depicts incrementing a counter. The processnext passes to step 710, which depicts determining whether the counterhas exceeded a required value. The required value represents the numberof data points 608-620 that the system must store before performing thefunction of determining the maximum value of the position error signal.If the counter indicates that the required number of data points has notbeen stored, the process returns to step 702, which illustrates thedetection of a position error signal indicative of the distance betweenan expected position of a magnetic head relative to a track centerlineand an actual position of the magnetic head relative to the trackcenterline. Steps 704-708 are then repeated. If the counter indicatesthat the required number of data points 608-620 has been stored, theprocess then passes to step 712, which depicts determining the maximumof the absolute values of the position error signal that are stored asdata points 608-620 in the data structure.

The process then passes to step 714, which depicts determining whetherthe maximum of the absolute values of the position error signal exceedsa threshold value. Though some non-zero maximum absolute value of theposition error signal may exist at all times, the correlation betweenthe maximum of the absolute value of the position error signal and thelikelihood of a head-disk crash increases with the maximum of theabsolute value of the position error signal, and the threshold value towhich the determining step 714 compares the maximum of the absolutevalues of the position error signal represents a point at which themaximum of the absolute value of the position error signal correlates toa high likelihood of head-disk crash.

If the maximum of the absolute value of the position error signalexceeds the threshold value, the process next passes to step 716, whichillustrates propagating a warning signal. This warning signal, apredictive failure analysis warning, informs the system of thelikelihood of a head-disk crash. Once this signal is activated, thesystem can then take automatic measures to prevent data loss or canprompt the user with a predictive failure warning and instruct the userto take measures to protect the user's data. Measures that may be takenmanually or automatically include performing a backup of the magneticdata storage and retrieval system in question, discontinuing access tothe magnetic data storage and retrieval system and shutting down themagnetic data storage and retrieval system, or shutting down the dataprocessing system in which the magnetic data storage and retrievalsystem operates. The appropriate data loss prevention measures will varyon the basis of the operational requirements and environment of the dataprocessing system to which the magnetic data storage and retrievalsystem is attached. If the maximum of the absolute value of the positionerror signal does not exceed the threshold value, the process nextpasses to step 700, which depicts an initiation sequence. In someembodiments of the invention, the initiation sequence will involvewaiting for the hard drive to enter its idle time function, or theprocess may be triggered by other system events ranging from an internaltiming trigger to manual input from a user of the system.

With reference to FIG. 8, a high-level flowchart for a process ofpredicting and warning of an impending head-disk crash on the basis ofthe square of the position error signal in accordance with a secondalternative embodiment of the present invention is depicted. The processbegins at step 800, which depicts an initiation sequence. In someembodiments of the invention, the initiation sequence will involvewaiting for the hard drive to enter its idle time function, or theprocess may be triggered by other system events ranging from an internaltiming trigger to manual input from a user of the system. After theprocess has been triggered and the initiation sequence portrayed in step800 has run, the process then passes to step 802, which illustrates thedetection of a position error signal indicative of the distance betweenan expected position of a magnetic head relative to a track centerlineand an actual position of the magnetic head relative to the trackcenterline. The process next passes to step 804, which depictsdetermining the square of the position error signal.

This embodiment of the invention functions on the basis of an observedcorrelation between the square of the position error signal and theoccurrence of disk-head crash. For many magnetic data storage andretrieval systems, if the square of the position error signal exceeds agiven value, a high likelihood of head-disk crash exists. That thesquare of the position error signal exceeds a given value serves as aprecursor to disk failure.

The process next passes to step 806, which illustrates storing thesquare of the position error signal. The position error signal willtypically be stored in a data structure 600 such as that portrayed inFIG. 6. In a typical embodiment, each of several storage levels 602-606will represent one or more testing periods, each of which will containseveral data points 608-620. A typical embodiment will involve theplacement of a series of data points 608-620 in one or more storagelevels. In step 806, the process stores an individual square of theposition error signal in an individual data point. The process thenpasses to step 808, which depicts incrementing a counter. The processnext passes to step 810, which depicts determining whether the counterhas exceeded a required value. The required value represents the numberof data points 608-620 that the system must store before performing thefunction of determining the maximum value of the position error signal.If the counter indicates that the required number of data points has notbeen stored, the process returns to step 802, which illustrates thedetection of a position error signal indicative of the distance betweenan expected position of a magnetic head relative to a track centerlineand an actual position of the magnetic head relative to the trackcenterline. Steps 804-808 are then repeated. If the counter indicatesthat the required number of data points 608-620 has been stored, theprocess then passes to step 812, which depicts determining the maximumof the squares of the position error signal that are stored as datapoints 608-620 in the data structure.

The process then passes to step 814, which depicts determining whetherthe maximum of the squares of the position error signal exceeds athreshold value. Though some non-zero maximum square of the positionerror signal may exist at all times, the correlation between the maximumof the square of the position error signal and the likelihood of ahead-disk crash increases with the maximum of the square of the positionerror signal, and the threshold value to which the determining step 814compares the square of the position error signal represents a point atwhich the maximum of the square of the position error signal correlatesto a high likelihood of head-disk crash.

If the maximum of the square of the position error signal exceeds thethreshold value, the process next passes to step 816, which illustratespropagating a warning signal. This warning signal, a predictive failureanalysis warning, informs the system of the likelihood of a head-diskcrash. Once this signal is activated, the system can then take automaticmeasures to prevent data loss or can prompt the user with a predictivefailure warning and instruct the user to take measures to protect theuser's data. Measures that may be taken manually or automaticallyinclude performing a backup of the magnetic data storage and retrievalsystem in question, discontinuing access to the magnetic data storageand retrieval system and shutting down the magnetic data storage andretrieval system, or shutting down the data processing system in whichthe magnetic data storage and retrieval system operates. The appropriatedata loss prevention measures will vary on the basis of the operationalrequirements and environment of the data processing system to which themagnetic data storage and retrieval system is attached. If the maximumof the square of the position error signal does not exceed the thresholdvalue, the process next passes to step 800, which depicts an initiationsequence. In some embodiments of the invention, the initiation sequencewill involve waiting for the hard drive to enter its idle time function,or the process may be triggered by other system events ranging from aninternal timing trigger to manual input from a user of the system.

Although aspects of the present invention have been described withrespect to a computer system executing software that directs thefunctions of the present invention, it should be understood that presentinvention may alternatively be implemented as a program product for usewith a data processing system. Programs defining the functions of thepresent invention can be delivered to a data processing system via avariety of signal-bearing media, which include, without limitation,non-rewritable storage media (e.g., CD-ROM), rewritable storage media(e.g., a floppy diskette or hard disk drive), and communication media,such as digital and analog networks. It should be understood, therefore,that such signal-bearing media, when carrying or encoding computerreadable instructions that direct the functions of the presentinvention, represent alternative embodiments of the present invention.

1. A method of predicting head-disk interaction in a magnetic datastorage and retrieval system, comprising: detecting a position errorsignal amplitude indicative of the distance between an expected positionof a magnetic head relative to a track centerline and an actual positionof the magnetic head relative to the track centerline; filtering andrectifying the position error signal amplitude to generate a sway modesignal amplitude indicative of an oscillation of the actual position ofthe magnetic head relative to the track centerline in a selectedfrequency range; determining an absolute value of the sway mode signalamplitude; determining whether the absolute value of the sway modesignal amplitude exceeds a threshold value; and responsive todetermining that the absolute value of the sway mode signal amplitudeexceeds the threshold value, propagating a warning signal.
 2. The methodof claim 1, wherein the filtering step further comprises: testing themagnetic data storage and retrieval system to determine a unique swaymode frequency range; and programming a programmable filter to excludesignals other than those near the unique sway mode frequency.
 3. Amethod of predicting head-disk interaction in a magnetic data storageand retrieval system, comprising: detecting a position error signalamplitude indicative of the distance between an expected position of amagnetic head relative to a track centerline and an actual position ofthe magnetic head relative to track centerline, wherein the detectingstep further comprises detecting the position error signal during anidle time function; filtering and rectifying the position error signalamplitude to generate a sway mode signal amplitude indicative of anoscillation of the actual position of the magnetic head relative to thetrack centerline in a selected frequency range; testing the magneticdata storage and retrieval system to determine a unique sway modefrequency range; programming programmable filter to exclude signalsother than those near the unique sway mode frequency; determining anabsolute value of the sway mode signal amplitude; determining whetherthe absolute value of the sway mode signal amplitude exceeds a thresholdvalue; and responsive to determining that the absolute value of the swaymode signal amplitude exceeds the threshold value, propagating a warningsignal.
 4. An apparatus for predicting head-disk crash in a magneticdata storage and retrieval system, comprising: means for detecting aposition error signal amplitude indicative of the distance between anexpected position of a magnetic head relative to a track centerline andan actual position of the magnetic head relative to the trackcenterline; means for filtering and rectifying the position error signalamplitude to generate a sway mode signal amplitude indicative of anoscillation of the actual position of the magnetic head relative to therecording surface in a selected frequency range; means for determiningan absolute value of the sway mode signal amplitude; means fordetermining whether the absolute value of the sway mode signal amplitudeexceeds a threshold value; and means for, responsive to determining thatthe absolute value of the sway mode signal amplitude exceeds thethreshold value, propagating a warning signal.
 5. The apparatus of claim4, wherein the means for filtering further comprises: means for testingthe magnetic data storage and retrieval system to determine a uniquesway mode frequency range; and means for programming a programmablefilter to exclude signals other than those near the unique sway modefrequency range.
 6. An apparatus for predicting head-disk crash in amagnetic data storage and retrieval system, comprising: means fordetecting a position error signal amplitude indicative of the distancebetween an expected position of a magnetic head relative to a trackcenterline and an actual position of the magnetic head relative to thetrack centerline, wherein the means for detecting further comprisesmeans for detecting the position error signal during an idle timefunction. means for filtering and rectifying the position error signalamplitude to generate a sway mode signal amplitude indicative of anoscillation of the actual position of the magnetic head relative to therecording surface in a selected frequency range; means for determiningand absolute value of the sway mode signal amplitude; means for testingthe magnetic data storage and retrieval system to determine a uniquesway mode frequency range; means for programming a programmable filterto exclude signals other than those near the unique sway mode frequencyrange means for determining whether the absolute value of the sway modesignal amplitude exceeds a threshold value; and means for, responsive todetermining that the absolute value of the sway mode signal amplitudeexceeds the threshold value, propagating a warning signal.
 7. Theapparatus of claim 4, wherein the apparatus for predicting head-diskcrash in a magnetic data storage and retrieval system further comprises:an outer housing or base containing a plurality of stacked, parallelmagnetic disks, which are closely spaced apart; an actuator comprising aplurality of stacked, parallel actuator arm/suspensions in the form of acomb that is pivotally mounted to the base about a pivot assembly; acontroller, mounted to the base, for selectively moving the comb ofarm/suspensions relative to disks and monitoring and providing commandinputs to the actuator; and one or more magnetic read/write transducers.8. A computer program product in a computer usable medium for predictinghead-disk crash in a magnetic data storage and retrieval system,comprising: instructions on the computer usable medium for detecting aposition error signal amplitude indicative of the distance between anexpected position of a magnetic head relative to a track centerline andan actual position of the magnetic head relative to the trackcenterline; instructions on the computer usable medium for filtering andrectifying the position error signal to generate a sway mode signalamplitude indicative of an oscillation of the actual position of themagnetic head relative to the track centerline in a selected frequencyrange; instructions on the computer usable medium for determining anabsolute value of the sway mode signal amplitude; instructions on thecomputer usable medium for determining whether the absolute value of thesway mode signal amplitude exceeds a threshold value; and instructionson the computer usable medium for, responsive to determining that theabsolute value of the sway mode signal amplitude exceeds the thresholdvalue, propagating a warning signal.
 9. The computer program product ofclaim 8, wherein the instructions for filtering further comprise:instructions on the computer usable medium for testing the magnetic datastorage and retrieval system to determine a unique sway mode frequencyrange; and instructions on the computer usable medium for programming aprogrammable filter to exclude signals other than those near the uniquesway mode frequency range.
 10. A computer program product in a computerusable medium for predicting head-disk crash in a magnetic data storageand retrieval system, comprising: instructions on the computer usablemedium for detecting a position error signal amplitude indicative of thedistance between an expected position of a magnetic head relative to atrack centerline and an actual position of the magnetic head relative tothe track centerline, wherein the instructions for detecting furthercomprise instructions on the computer usable medium for detecting theposition error signal amplitude during an idle time function;instructions on the computer usable medium for filtering and rectifyingthe position error signal to generate a sway mode signal amplitudeindicative of an oscillation of the actual position of the magnetic headrelative to the track centerline in a selected frequency range;instruction on the computer usable medium for determining an absolutevalue of the sway mode signal amplitude; instructions on the computerusable medium for testing the magnetic data storage and retrieval systemto determine a unique sway mode frequency range; instructions on thecomputer usable medium for programming a programmable filter to excludesignals other than those near the unique sway mode frequency range;instructions on the computer usable medium for determining whether theabsolute value of the sway mode signal amplitude exceeds a thresholdvalue; and instructions on the computer usable medium for, responsive todetermining that the absolute value of the sway mode signal amplitudeexceeds the threshold value, propagating a warning signal.